Heretofore, most fluid containment tanks have been comprised of a single-wall construction including a single-wall side wall and a shell bottom for containing the fluid and for supporting the weight of the fluid in the tank. The shell bottom normally rests on wooden, steel beam or concrete supports resting on pylons or a ground support. When a toxic or other ground water damaging or medically hazardous material is to be confined, double wall containments have been mandated. Thus in the case of certain waste water treatment processes the U.S. Environmental Protection Agency (EPA) have required a double-wall containment. Water treatment equipment as mandated by the EPA typically comprise double-wall barriers made up of two totally separate tanks. As an example, a concrete floor with peripheral vertical concrete walls will be lined with a metal liner or painted. Inside this large normally open-to-the-atmosphere containment, a steel elevated tank will be erected and utilized. Any leakage from the elevated tank will be captured and monitored by means of the concrete containment.
Other equipment has utilized double containment barriers. Scrubbers used in the Power industry utilize a liner (a corrosion-resistant thin material) laid directly against a heavier structural load carrying shell (noncorrosion resistant). Leakage is monitored in the annular area. Oil tankers also utilize double-barrier containments.